What is a Sea Slug?

Steve R.

A hermaphroditic underwater creature, a sea slug can typically be located on coral or rocks in the sea. Also known as a sea cucumber, a sea slug can vary in length from an inch (about 2.5 centimeters) to one foot (about 31 centimeters). More than 3,000 varieties of the species exist and come in various of colors. The sea creature belongs to the gastropod family and can live anywhere from six weeks to one year.

Crabs are natural predators of sea slugs.
Crabs are natural predators of sea slugs.

Technically, sea slugs are nudibranches, which is Latin for "naked gills." Many varieties of sea slug carry their gills on their backs. When the creatures are young, they shed their shells, which never grow back.

Turtles will sometimes prey on sea slugs.
Turtles will sometimes prey on sea slugs.

While sea slugs are tiny creatures, they are not defenseless. Sea slugs are not affected by the paralyzing stingers of potential predators, such as sea anemones or corals. Instead, a sea slug soaks the stingers into its body and will use the weapons against any creature that tries to attack it.

A sea slug is colloquially known as the sea cucumber.
A sea slug is colloquially known as the sea cucumber.

Similar to skunks, sea slugs can secrete an odorous substance to ward off attacks. Some species of sea slugs possess tentacles, which are used for defense. Brightly colored creatures, sea slugs use their colors to blend into the environment and hide from predators. Sea slugs also can use their vibrant colors to present themselves as something that would be dangerous for would-be predators to eat.

Despite their numerous defense mechanisms, sea slugs do still fall prey to some creatures. Sea spiders, turtles, sea stars, lobsters, and crabs are natural predators of sea slugs. Sea slugs also are harvested by humans.

Slow moving creatures, sea slugs move along the sea floor looking for food. The creatures possess small teeth in their mouths, which are located on the underside of their heads, and they use chemical signals to find food. Sea slugs feed on barnacles, sponges, snails, and plankton. Some sea slugs even feed on other sea slugs.

Containing both male and female sex traits, nudibranches lay thousands of eggs at least once a year, depending on food supply. Eggs attach to rocks or sand in crevices. After a few weeks, the eggs are fertilized and then hatch.

Sea slugs are often kept in saltwater aquariums to help reduce the level of algae in the tanks. The creatures are also of interest to humans for their potential in healing. Scientists have studied the creatures to see how chemicals in their bodies can help with heart, bone, and brain aliments.

A sea slug is also known as a sea cucumber, and humans have interest in them for their possible healing powers..
A sea slug is also known as a sea cucumber, and humans have interest in them for their possible healing powers..

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We had sea slugs in our canals on Venice Beach about 14 years ago. Then they disappeared and came back this year. Do you know why that would have happened?


Thanks to all of you for the great information on sea slugs. You have all helped me out tremendously. That's why I love WiseGeek!!!!


Sea slugs are actually quite fascinating. They creep along the bottom of the ocean floor or cling to submerged vegetation, usually in water just below the low tide line. Some of the species swim on the surface of an open ocean.

They are regarded by many as one of the most beautiful marine animals, contrary to their yucky sounding name! They often have feathery structures called ceratia on their back. The ceratis are usually in a contrasting color.

If any of you have an opportunity, you should look at some pictures of the sea slugs. They are quite beautiful and their color is very vibrant.


@momothree: The sea slug is a marine gastropod mollusk. They are classified in the phylum Mollusca, class Gastropoda, sublass Opisthobranchia, and order Nudibranchiata. I hope that helps you and good luck with your project.


First, I love your articles on WG! They are very helpful. I am a Biology student and I have to do a report on sea slugs.

I need to know the sea slug phylum, class, subclass, and order. Can anyone help me out?

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